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Increasing Agricultural Water Productivity Through Better Crop Nutrition

Congress: 2015
Author(s): Dejene Eticha (Duelmen, Germany), Joachim Lammel
Yara GmbH & co. KG1

Keyword(s): Sub-theme 6: Links with the energy, food and environmental sectors,
AbstractAgriculture utilizes the largest share of global fresh water resources. As the world population steadily increases, agricultural production should also be increased in order to ensure global food security. It is estimated that agricultural production has to be doubled by 2050 to cover the growing demand for food and agricultural raw materials. The increase of agricultural production without massive expansion of cropping area and overexploitation of regional freshwater resources requires a combination of suitable approaches enabling sustainable intensification. Global yield assessment of major food crops indicates that there are huge gaps between observed yields and attainable yields in a given region. Closing yield gaps can be achieved mainly through improved nutrient and water management (Mueller, et al., 2012). Water is lost from a crop land through evapotranspiration which is a combination of two separate processes, namely, evaporation from the soil and transpiration from the plant. Only about 15-30% of the rainfall or irrigation water is transpired by the crop for dry matter production while most of the water used for irrigation is lost during storage and conveyance, by runoff and drainage, and evaporation from the soil (Wallace and Gregory 2002). These losses can be substantially reduced by employing efficient irrigation techniques and sound crop nutrient management. The objective of this work was to study the effect of nitrogen supply on grain water productivity of wheat. In addition, the significance of nitrogen nutrition on crop canopy development and reduction of bare-soil evaporation was investigated. Wheat plants were grown in glass house at different N supply levels. Pots were weighed and watered once or twice a day to maintain the moisture level at 55-65% water holding capacity. The daily crop water-consumption was recorded at each watering event. Plants were harvested at physiological maturity and grain water productivity was calculated from grain yield and cumulative water consumption. In addition, field trials were conducted to determine bare-soil evaporation under crop canopies with different levels of N fertilizer application. For this purpose mini-lysimeters were installed in the plots and daily evaporation loss was recorded. The change in soil moisture in the rooting zone and climatic data were used to calculate field water balance. Nitrogen supply increased wheat grain yield and water productivity. There was close positive correlation between grain yield and water productivity across N supply levels. Under low N supply, about 600 liters (L) of water were needed to produce 1 kg of grain while at optimal N supply only 380 L were required. That means, using the same quantity of water, more crop yield can be obtained with optimal nutrient supply than nutrient deficiency. Our lysimeter study showed that nitrogen supply reduced bare-soil evaporation. The seasonal evapotranspiration did not significantly differ across N supply levels but the percentage of unproductive water loss as bare-soil evaporation was significantly higher at low N (60%) compared to optimal N (20%) supply. Under optimal N supply, a larger proportion of the seasonal available water was transpired by the crop and contributed to yield formation whereas under N deficient condition, more water was lost through soil evaporation. Optimal crop nutrition enables better early growth and quicker canopy closure which reduces bare-soil evaporation. In addition, well-nourished plants develop a more vigorous root system which takes up water from deeper soil layers and reduce drainage losses. The drainage below the rooting zone is unproductive water loss from a crop production perspective but it contributes to groundwater recharge. However, reducing crop production intensity will not translate in proportional increases of groundwater recharge since more water will be lost through bare-soil evaporation. In conclusion, optimally nourished crops produce more biomass and grain yield per unit of transpired water than nutrient deficient crops. Therefore, sound nutrient management is as an integral part of water management in agriculture with the focus on optimizing crop water productivity and avoiding freshwater pollution. 1. Mueller ND, Gerber JS, Johnston M, Ray DK, Ramankutty N, Foley JA (2012) Closing yield gaps through nutrient and water management. Nature 490:254-257. 2. Wallace JS, Gregory PJ (2002) Water resources and their use in food production systems. Aquatic Sciences 64: 363-375
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